The innate immune response is a critical component of host defense against infection. Antimicrobial peptides are an evolutionarily conserved class of innate immune effectors with well-described anti-bacterial activity;however, their role in anti-viral immunity is less well understood. Recently, I described the mechanism by which one family of antimicrobial peptides, a-defensins, inhibit human adenovirus infection. I found that defensins block adenovirus entry by binding to the virus capsid and preventing uncoating in and escape from the endosome. This finding, in conjunction with recent work on defensin-mediated inhibition of human papillomavirus infection showing that this virus is also blocked at the stage of endosome escape, suggests that a-defensins block non-enveloped virus entry through common mechanisms. This proposal will explore the hypothesis that defensins inhibit non-enveloped virus infection through the recognition of structurally conserved motifs on the virus capsid by biochemically defining the molecular basis for the interaction between a-defensins and adenovirus. In addition, the impact of defensins on the recognition of the incoming virus particle by cellular innate immune sensors will be explored. For adenovirus, recognition of the viral DNA during entry has been shown to stimulate a Toll-like receptor 9-dependent and -independent type I interferon response. Inhibition of virus infection by defensins provides a unique opportunity to explore the role of virus uncoating in this process. These studies will provide valuable insights into the mechanism of defensin-mediated inhibition of a model non-enveloped virus infection and will form the basis for an investigation into whether the molecular mechanism of inhibition by defensins applies to other non-enveloped viruses. Moreover, they will be instrumental in establishing a model to elucidate, for the first time, the role of defensins in anti-viral immunity in vivo. RELEVANCE: These studies will determine how one component of the human immune system blocks adenovirus infection by preventing the virus, once it has entered the cell, from reaching the nucleus. A detailed understanding of how the immune system blocks adenovirus infection may uncover a common way to inhibit other virus infections and may guide the design of antiviral drugs.